I concur Handbrake is a terrific video converter and my first choice when required. Free, highly configurable and does an excellent job. Nevertheless, it also drops a noticeable proportion of frames, when converting from WebM to other formats, causing sync issues, but, to be honest, that seems to be a common ocurrence, regardless of the converter used.

So my advice, when some post-production work with a third-party video edition application is needed, is to try to avoid any intermediate conversion step.

ars longa vita brevis - Hippocrates (attributed)

If you want to tell jokes then use Muvizu; if you want to make 'Movies', use iClone; but if you want to tell stories, use Moviestorm - PrimaveraNZ

I have used Handbrake and tried every configuration I could think of. And frame loss happens all the time: if you import the converted movie into, say, Sony Movie Studio, the video event is clearly shorter than the audio event, many times in a conspicuous magnitude. If audio work is exclusively done inside your video editing tool, it makes no problem, otherwise some resyncing work might be necessary.

On the other hand, I've tried almost every other converter I've found and all of them behave the same. Most probably they use the same base library for their codecs when dealing with the VP8/VP9 video encoding.

ars longa vita brevis - Hippocrates (attributed)

If you want to tell jokes then use Muvizu; if you want to make 'Movies', use iClone; but if you want to tell stories, use Moviestorm - PrimaveraNZ

Avidemux is a open source video editor that does simple video editing but it also allows you to re-mux videos and it does have a webm muxer, so it can also do video converting also. It has versions for Windows, Linux and Mac OS X.

I have used Handbrake and tried every configuration I could think of. And frame loss happens all the time: if you import the converted movie into, say, Sony Movie Studio, the video event is clearly shorter than the audio event, many times in a conspicuous magnitude. If audio work is exclusively done inside your video editing tool, it makes no problem, otherwise some resyncing work might be necessary.

On the other hand, I've tried almost every other converter I've found and all of them behave the same. Most probably they use the same base library for their codecs when dealing with the VP8/VP9 video encoding.

IIRC, I think a lot of encoders tend to use the FFMPEG libraries, some use the memcoder libraries. I know that the encoder that Google created for webm is known as libvpx, FFMPEG uses libvpx for webm encoding, For VP8 encoding, FFMPEG use libvpx, VP9 is done using libvpx-vp9.